Reinforced polymeric composites

ABSTRACT

A high strength reinforced composite has an outer polymeric skin and an inner polymeric foam core chemically and mechanically bonded together at a high modulus, three dimensional interface comprising longitudinally continuous strands, transversely continuous and randomly arrayed transverse strands, and randomly inclined short strands having end portions embedded in both the skin and the core.

RELATED APPLICATION

This patent application is a continuation-in-part application of U.S.patent application Ser. No. 179,479 filed on Apr. 8, 1988, now U.S. Pat.No. 4,828,897.

BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of reinforced polymericarticles and, in particular, to continuously molded compositescomprising a polyurethane core and polyurethane skin structurallyintegrated at a three dimensional high modulus interface.

Foamed polyurethane products having integral reinforcements forimparting increased strength to a core have been formed in both batchand continuous processes. For example, in U.S. Pat. Nos. 4,163,824 and4,073,840, there is disclosed a method and apparatus for producingfiber-reinforced foam articles wherein randomly oriented fiber filamentsare dispersed throughout a core. This produces a foamed product ofsubstantially uniform density. Another batch process is disclosed inU.S. Pat. No. 4,130,614 wherein woven glass mats reinforce the top andbottom surfaces of a foamed article with the glass mats capturedentirely within a higher density outer foam layer which surrounds alower density inner core. The major surfaces may include a film layeradhered to the outer foam layer. A similar material is also disclosed inU.S. Pat. No. 3,895,159 wherein a glass fabric is embedded in at leastone noncellular surface layer. Continuous processes have been disclosedfor the manufacture of foamed articles, particularly laminated foams.For instance, U.S. Pat. Nos. 3,686,047; 4,496,625; 4,555,442; Re.30,984; 3,142,864; and 3,903,346, disclose continuous foam laminateswherein structural facing sheets of materials such as foils, film, andthe like are laminated to the inner foam core during an open-endedforming process.

In the above approaches to reinforcing the foam, certain physicalcharacteristics are improved while others are not. The laminates improveflexure strength and to an extent longitudinal compressive strength incomparison with the foam core alone. However, only an adhesive bond andnot a mechanical bond is effected between the foam and the laminate.Accordingly, this presents a relatively weak shear interface,particularly under high cyclical loadings. Such articles are prone tofracturing at the interface with a resultant loss of product integrity.It would be desirable to provide, in view of the foregoing limitations,a reinforced polymeric composite system with improved static and dynamiccharacteristics as a load bearing member which system provides increaseddesign flexibility within existing thermoset chemistry and can beaccurately produced in a continuous process.

BRIEF SUMMARY OF THE INVENTION

The present invention provides reinforced foam composite systemsovercoming the aforementioned deficiencies of prior reinforced foamwhich has broad utilization as a load bearing member for static as wellas dynamic applications. In particular, such composite systemsout-perform wood or wood substitutes in compressive strength, flexurestrength and impact strength.

In its broadest aspect, the invention provides a continuous process formaking a reinforced foamed composite by structurally integrating a threedimensional high modulus strand material interface into both an innerand outer polymeric substrate. The process is designed to pullcontinuous strands or mats through a continuous cavity while placing acoating on the outside surface, a foam core in the interior with aninterface comprising high modulus chopped strands and the continuousstrands in three dimensional orientation locking the coating with thecore. This process makes a reinforced polymeric composite in acontinuous process to predetermined cross sectional configurations.Substantial strength in the direction transverse to the longitudingalstrands may be provided by continuous cross or transverse strands. Asopposed to woven mats which are not comparable tensile bearing membersin composite, the continuous cross strands provide uniform strengthcharacteristics in both the longitudinal and transverse directions.

More particularly, the process provides a plurality of continuous moldsthat traverse a pathway. The molds have opposed surfaces thereondefining an open ended cavity of the predetermined cross sectionalconfiguration. Continuous thin, flexible mold release films are fedcojointly with the molds and overlay the opposed surfaces defining thecavity. A thin coating of a first non-volatile liquid thermosetpolymeric composition, such as a rigid polyurethane, is applied to eachof the mold release films on the inwardly facing surfaces thereof. Aplurality of continuous glass strands, such as fiberglas, are fed alongsaid pathway cojointly with the mold release films and applied lightlyonto each coating. A random array of short chopped high modulus strands,such as fiber glass, are dispersed in transverse layers on thecontinuous glass, with both the continuous and chopped glass strandsbeing wetted at least partially by both compositions. A second foamable,non-volatile liquid thermoset polymeric composition, such as anisocyanateurethane is dispersed into the space between the inwardlyfacing surfaces of the strands. The coating quickly sets at an outerskin while the remainder thereof is maintained in a viscous statepermitting the coating to wet and penetrate the strands until subsequentto the conforming. Thus the glass is partially wetted by bothcompositions. As a result, the strands are captured at the interfacebetween the compositions. Sufficient blowing agent is provided in thethe second reactant composition for the to at least partially penetratethe strands and to embed ends of the chopped strands in bothcompositions to form a three dimensional glass network of high moduluswhich structurally integrates the coating with the core. Wherecontinuous cross or transverse strands are incorporated in thecomposite, the same are added upstream of chopped glass.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects and other benefits and advantages of the presentinvention will become apparent upon reading the detailed description ofthe preferred embodiments taken in conjunction with the accompanyingdrawings in which;

FIG. 1 is a schematic side elevational view of the continuous processfor making a reinforced foamed composite according to the presentinvention;

FIG. 2 is a cross sectional view of a composite produced in accordancewith the process of FIG. 1;

FIG. 3 is a schematic view of the process illustrated in FIG. 1 showingthe various reaction zones therein;

FIG. 4 is a transverse cross sectional view of the mold segments for thecomposite;

FIG. 5 is a cross sectional representation at composite failure, and

FIG. 6 is a graph relating deflection versus load for actual andpredicted composites;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the drawings and in particular to FIGS. 1 and 2, there isshown a process for making a reinforced foamed composite 10 in acontinuous casting machine, generally indicated by the numeral 12. Thecomposite 10, as illustrated in greater detail in FIG. 2, comprises amolded structure of a skin 20 comprising an outer surface 22 and aninner base 24, an inner core 26 including a random array of high modulusstrands 28, and a three dimensional network of high modulus strands,generally indicated by the reference numberal 30, which mechanically andchemically bonds the core 26 to the skin 20 to form a unitary structure.As will be hereinafter described in greater detail, the network 30comprises continuous strands 32, longitudinally disposed, and a layer ofchopped strands 34, disposed randomly transversely, with portions 36 ofthe strands 34 having ends embedded in both the skin 20 and the core 26.

The process for making the above described composite 10 is schematicallyillustrated in FIG. 1. Therein a pair of opposed continuous molds 40, 42traverse a generally horizontal pathway 44 between an entrance end 46and an exit end 48. The molds 40, 42, as shown in FIG. 5, have opposedinner surfaces 50 thereon thus defining an elongated open-endedhorizontal cavity 52 along the pathway 44 of the predetermined crosssectional configuration. As will become hereinafter apparent, the molds40, 42 may be configured to define cross sections of desired shape,whether symmetrical or non-symmetrical. Further, the belts 40, 42 may beperiodically interrupted to provide composites of predetermined discretelengths. The process is moreover amenable to making predictably productsof desired strength properties in a wide range of configurations throughprocess control involving composition, density, thickness, width,elastic modulus, and skin thickness as will he exemplified in greaterdetail below.

A pair of continuous thin, flexible mold release films 60, 62 are fedcojointly with the molds 40, 42 and overlie the opposed inner surfaces50 defining the cavity 52. A thin upper coating 64 and lower coating 65is applied to each of the mold release film 60, 62, respectively, on theinwardly facing surfaces thereof. A plurality of high modulus continuouslongitudinal strands 66, 68 are fed longitudinally along said pathway 44cojointly with the films 60, 62 and onto the coating 64. The continuousglass strands 66, 68 are lightly tensioned so as to be partially wettedby the coating 64. A random array of high modulus, chopped strands 70,71 are dispersed in layers on the continuous glass strands 66, 68,respectively, downstream of the coating 64. A formable core 74 isdispersed in the space between the inwardly facing surfaces of thelayers of chopped glass strands 70, 71. In the described embodiment, theskin 2 is a high density urethane and the core 74 is a urethaneformulation comprising a polyol, a catalyst system, a filler and ablowing agent, in sufficient proportions to effect a foam matrix ofsufficient volume to conform the films 60, 62 to the configuration ofthe opposed surfaces 50, 51 of the molds 40, 42. The strands aremonofilament fiber glass.

In a modification of the thus far described composite and process, aplurality of high modulus continuous transverse strands 69a, 69b mayalso be fed longitudinally along said pathway 44, immediately downstreamof the strands 66, 68, cojointly with the films 60, 62 and onto thecoating 64. A composite incorporating the transverse strands differsfrom the aforementioned composite in the addition of a longitudinalarray of continuous cross or transverse strands extending transverselyof the composite in abutting relation with the continuous longitudinalstrands. These transverse strands also form a part of the threedimensional network 30 of high modulus strands. In this case, thecomposite 10 comprises a molded structure of the skin 20 comprising theouter surface 22 and inner base 24, and inner core 26 including a randomarray of high modulus continuous longitudinal strands 28, and the threedimensional network 30, which mechanically and chemically bonds the core26 to the skin 20 to form a unitary structure. The network 30 comprisesthe longitudinal strands 32, the transverse strands 33, and the layer ofchopped strands 34 disposed randomly transversely with the strands 33.Portions 36 of the strands 34 have ends embedded in both the skin 20 andthe core 26.

Examples of polymers suitable for the coating and the core arepolyurethanes, polyesters, polyamides, epoxies, acrylics, silicones,phenolics and other like non-volatile liquid monomers. Examples of highmodulus strands are fiber glass, carbon fibers and other strand materialhaving a high elastic modulus. The strands are preferably conventionallycoated to promote adhesion between the strands and the substrates.Suitable fillers include calcium carbonate, alumina trihydrate, mica,calcium sulfate, talc, calcium silicate, silica and other like,relatively inexpensive organic and inorganic materials.

More particularly, the machine 12 manufactures the composite 10 incontinuous lengths to the cross section prescribed by the configurationof the molds 40, 42. Adjacent the exit end 48 of the machine 12, thecomposite 10 may be severed to desired length by a suitable cuttingapparatus, such as a shear or saw, synchronized to the belt speed. Thecutting apparatus may be manually or automatically controlled to severthe composite 10 on a continuous basis to constant or variable lengths.

The process 12, as shown in FIG. 3, comprises three basic reactionzones, each of which is critical to the integrity of the resultantproduct: Zone A Wherein the components are delivered and initialreactions proceed: Zone B wherein the subsequent chemical reactionsproceed; and Zone C wherein the composite is cured.

The continuous molds 40, 42 in the preferred embodiment comprisecontinuous tracks of pivotally interconnected segments. Referring toFIG. 4, the individual segments are each machined at the inner surfaces50, 51 for the desired configuration. The upper mold 42 is rotatablysupported by rollers 82. The lower mold 40 is similarly rotatablysupported by rollers 86. The upper mold 42 is generally coextensive withZone B and Zone C. The lower mold 40 is generally coextensive with ZonesA through C. The molds 40, 42 abut in Zone B and zone C to establish theopen ended molding cavity 52 between the entrance and 46 and the exitend 48. The molds 40, 42 may be hydraulically or mechanically biased tomaintain closure under the foaming pressures experienced in the process.

The molds 40, 42 are connected to conventional electrical drive andcontrol units, not shown, to cojointly drive the molds at the same, butadjustable, speed. Preferably and as will become apparent below, thespeed of the belts can be variably controlled in a conventional mannerby the drive units to control the process in conjunction with varyingthe components and attendant process conditions.

The inner surfaces of the molds 40, 42 are isolated from the compositereactant components by the mold release films 60, 62. The lower moldrelease film 60 is rotatably supported in a supply roll 90 adjacent theentry roller 86 for the lower mold belt 40. The upper mold release film62 is rotatably supported in a supply roll 92 above the upper mold belt42 and downstream of the entrance roller 82 therefor. The mold releasefilms 60, 62 are driven through the process apparatus by the molds 40,42 under the clamping loading of the abutting mold sections. The uppermold release film 62 is stripped from the molded composite at an take-uproll 94 located adjacent the exit end 48 of the molding cavity 52. Thelower mold release film 60 is stripped from the molded composite at alower take-up roll 96 located adjacent the exit end of the moldingcavity 52.

In a commercial embodiment of the process 12, the molds 40, 42 arecomprised of a continuous chain of hingedly interconnecting moldsegments. Inasmuch as the interface of the segments define a transverseparting line, the mold release films 60, 62 present barrier to theoutflow of reactants thereby significantly eliminating transverseflashing. As the films are not required for composite strength, they arenon-adherent to both the composite and the molds, so as to be readilyremovable at the exit end. A polyetheylene film is used in the describedembodiment. However, it will be appreciated that for decorative purposesor improved strength the films may be, adherent to the composite 10thereby eliminating the need for the removal thereof.

It will also be appreciated that the molds 40, 42 can be continuouspieces, in the form of a belt, having integrally formed mold cavitysurfaces. For instance, extruded flexible materials may be joined end toend to form a belt of the desired length and configuration. It will alsobe appreciated that such a belt may overlie all or a portion of thesegments.

The coating 20 is a two component thermoset formulation and is appliedto the lower mold release film 60 adjacent the lower supply roll 90 atdispensing head 100 and to the upper mold release film 62 adjacent theupper supply roll 92 at dispensing head 102. The skin 20, depending onthe desired composite characteristics may be either rigid or foam. Thecoating components are delivered to the dispensing heads 100, 102 fromsupply tanks 104, 106 through supply lines by positive displacementpumps, thereby providing a metered and variable component supply inaccordance with the composite specifications. An additive may be blendedat the pumps 107 from supply tanks 108.

The lower continuous glass strands 66 are applied on the lower coating65 in bundles from a plurality of spools 110, remotely located andcollectively illustrated, at a location immediately downstream of thelower dispensing head 100. The upper continuous glass strands 68 areapplied on the upper coating 64 in bundles from a plurality of spools112, remotely located and collectively illustrated, at a locationimmediately downstream of the upper dispensing head 102.

Representative of suitable continuous strand material is Product No.625-11, R099 from CertainTeed Corp. supplied in the form of rovings at250 yards per pound.

The lower layer of chopped glass strands 70 are supplied in bundles fromspools 114, located remote from the process. The bundles proceed througha chopping device 116 for delivery directly in random array onto thelower coating 65 through a vertical chute 118. The upper layer ofchopped glass strands 71 are supplied from spools 120 in bundles, alsolocated remote from the process, and proceed through a chopping device122 for delivery directly in random array onto the upper surface of thecore 74 through a vertical chute 124. More particularly, continuousglass strand bundles are fed to the chopping devices for gravity flowthough the chutes in randomly arrayed transverse orientation. Thechopping devices are effective to sever the the strands into discretelengths of about 1 inch to about 2.5. This length range substantiallycontributes to core strength in comparison with the shorter length ofglass, 1 inch or under. In this connection, it has been observed that aslittle 75% less glass is required to provide comparable core strength.The gravity flow of the chopped glass onto the lower coating 65 and ontothe upper surface of the core 26 improves the three dimensionalorientation thereof in the structural interface between the core and thecoating.

Representative of suitable chopped glass strand material is Product No.290 from CertainTeed Corp. supplied in the form of continuous strandrovings at 207 yards per pound. The density of the layers of choppedglass strands 70, 71 is controlled between 0.02 lb/S.F. and 0.08lb/S.F., preferably around 0.04 lb/S.F., to minimize the overlapping andresultant buildup thereof. In other words, if too much chopped strand isdeposited, the chopped glass is not completely wetted by the reactants.As a result thereof under loading and particularly cyclic loading,delamination can readily occur between the coating 20 and the core 26.On the other hand, if too little chopped material is deposited, the core26 is interspersed with the coating 20, when the core foams or blows,the chopped strands separate and too readily pushes to the outer surfaceof the composite 10. In addition to producing a weak board, the same isalso cosmetically unacceptable. Moreover and as will be described ingreater detail below, portions of the chopped strands pivot from thetransverse plane such that the ends thereof are embedded in the coatingas well as the core. This forms the three dimensional network 30 therebysignificantly increasing the composite strength. More particularly,inasmuch as the chopped glass is randomly dispersed, some strands areinclined with respect to the continuous glass, while others are capturedin the continuous glass and turned upwardly by the foaming action. Somestrands are carried partially into the core 26 by the rising action ofthe foam and pressed into the coating 22 as it wets the continuousglass.

It will also be appreciated that if a discrete preformed component suchas a mat or felt is used for the outer surface of the composite 10, thechopped glass will nonetheless serve to maintain the separation of thecoating and the core. Inasmuch as the flexure strength of a coating andcore composite depends on the elastic modulus of the coating and itsthickness, keeping the low density core out of the coating maiximizesthe modulus thereof.

The continuous strands 66, 68 are lightly tensioned by means oftensioning rollers, not shown, sufficient to wet the strands on thesurface exposed to the coating but insufficient to cause extrusion ofthe coating material therethough or an embedding of a significantportion in the coating.

The molds 40, 42 in Zones B and C are surrounded by an enclosure 130.The interior of the enclosure 130 is heated or cooled by means of acoiled heating and/or cooling element 132, schematically illustrated.This temperature control permits the molds to be are heated andmaintained at a temperature for controlling the date at which thecoating sets for the purposes hereinafter described.

With particular reference to the process, as generally described above,the films 60, 62 are non-adherent to both the mold and the coating. Fora rigid thermoset coating and steel molds and a process operatingtemperature of between 150-160 degrees F, it is preferred to use as afilm and mold liner a low density polyethylene film. If higher reactiontemperatures are experienced in the process a higher meting point filmmay be selected. Moreover if a film, for decorative or strengthconsiderations, is desired as a laminate, it must be adherent to thecoating while obviously non-adherent to the molds. The coating ispreferably a high density non-volatile liquid thermoset polymer togetherwith minor amounts of a surfactant, and pigment. For a foam coating, afiller may be added together with the above reactants. These componentformulations and their associated reactions are well known in the art.Polyurethance and polyester formulations are exemplified in Table Ibelow.

                  TABLE I                                                         ______________________________________                                        TYPICAL COATING FORMULATIONS                                                  (parts by weight)                                                             ______________________________________                                        1. Polyurethane                                                               Component         Rigid      Foam                                             ______________________________________                                        A Polyol          100.0      100.0                                            B Isocyanate      101.2      101.2                                            C Surfactant      0.011      .011                                             D Filler          0.0        100.0                                            E Catalyst        0.0007     0.0009                                           ______________________________________                                         A-Pluracol No. 975 polyol manufactured by BASF                                BItem #M20S manufactured by BASF                                              CItem #DC193 manufactured by Dow                                              DAluminum Trihydrate manufactured by AluChem, Inc.                            EItem #T12 manufactured by Air Products                                  

    2. Polyester                                                                  Component         Rigid                                                       ______________________________________                                        A Polyester resin 100.0                                                       B Catalyst 1      1.0                                                         C Pigment 1       1.0                                                         D Pigment 2       10.0                                                        E Filler 1        30.0                                                        F Filler 2        30.0                                                        G Catalyst 2      2.0                                                         ______________________________________                                         A-Aropol 8438 manufactured by Ashland Chemical                                BCobalt octoate manufactured by Burton Plastics                               CTitanium dioxide                                                             DCarbon black                                                                 ECalcium carbonate                                                            FAlumina trihydrate                                                           GM.E.K. peroxide, Lupersol DHD9 manufactured by Lucidol Pennwalt Chemical                                                                              

The core is a foaming system of a well-known type comprising thermosetpolymers of the type used in the coating with surfactants, blowingagents and a catalyst system. A typical core formulation for apolyurethane and a polyester formulation, in parts by weight, inaccordance with the process described above is shown in Table II below.

                  TABLE II                                                        ______________________________________                                        Typical Core Formulation                                                      ______________________________________                                        1. Polyurethane                                                               Component               Parts                                                 ______________________________________                                        A Polyol                105.6                                                 B Filler                100.0                                                 C Surfactant            .01                                                   D Blowing Agent         .005                                                  E Catalyst 1            .001                                                  F Catalyst 2            .016                                                  G Catalyst 3            .05                                                   H Isocyanate            116.2                                                 ______________________________________                                         A-Pluracol No. 975 manufactured by BASF                                       BAlumina trihydrate manufactured by Aluchem Inc.                              CItem DC193 manufactured by Dow                                               DWater                                                                        EItem .T ]7 manufactured by Air Products                                      FItem 8154 manufactured by Air Products                                       GItem 8020 manufactured by Air Products                                       HPAPI 27 maunfactured by Dow                                                 2. Polyester                                                                  Component               Parts                                                 ______________________________________                                        A Polyester resin       100.0                                                 B Blowing Agent         1.5                                                   C Catalyst 1            10.0                                                  D Filler                50.0                                                  E Catalyst 2            1.5                                                   ______________________________________                                         A-Ampol No. 8438 manufactured by Ashland Chemical                             BLuperfoam Q 6920A manufactured by Lucidol Pennwalt Chemicals                 CCobalt napthanate                                                            DAlumina trihydrate                                                           EM.E.K. peroxide, Lupersol DHD9 manufactured by Lucidol Pennwalt Chemical                                                                              

With reference to polyurethane formulations, the core components aresupplied to a mixing head 138, located upstream of the entry end of thecavity, from through supply lines from a bank of five positivedisplacement meters 140. Four of the five meters 140 are fed by thesupply lines from reservoirs 142. The reservoirs 142 may contain asingle component or a mixture thereof. The other meter 140 is suppliedfrom a premix reservoir 144 from supply tanks 145, 146, 147 respectivelycontaining a polyol, filler and catalyst.

To enable this dynamic control, the positive displacement meters areused and provide the capability to make very small adjustments in thecatalyst and water ratios. All of the meters are hydraulically driven bya motor 150, timed together by a common spline shaft 152, such that theratios of the metered components remain the same, thereby delivering aflow to match belt speed. An example of metering pumps suitable for usein the process are disclosed in U.S. Pat. Nos. 3,920,223 and 4,339,233.

In addition to the blowing agents, surfactants, fillers, and catalystsemployed, other components such as fire retardants and pigments may beadded at the mixing head 138.

FIG. 1 illustrates five meters delivering to the mixing head. These arethe positive displacement type referred to above and driven by a commonmotor and shaft. The stroke of each may be changed during operation ofthe process. This stroke adjustment allows control of a discrete meter.Thus the chemical ratios may be changed without affecting the deliveryrate.

For the formulation shown in Table II, meter 140a is a premixed formulacontaining polyol, filler, surfactant and catalyst are delivered to themixing head. Meter 140b supplies a mixture of water and polyol forblowing the foam. Meter 140c delivers a flowing catalyst. The othermeters may be used for delivering any other desired additives. Theindividual meters permit easy cleaning and individual component controlfor the entire system.

For the typical polyurethane formulation, the ratios are 100 parts atmeter 140a, 3 parts at meter 140b and 2.7 parts at meter 140c. Thesemeters are calibrated and the mixes are scaled to deliver the activeingredient in correct proportion to the formulation. The meters arescaled to maintain the concentration of the active ingredients in thepolyol mixture so that the delivery rate of the active ingredient isabout 50% of the total at the meter.

It is particularly important to dynamically compute the isocyanaterequired per 100 parts of each meter mix using the hydroxal numbers forthe components of the specific mix. Using a calibration curve plus thedirect volume read out the isocynate stroke on each meter is adjusted tothe desired ratio.

With the above typical formulations and variations therefrom, a widerange of products can be manufactured with cores having densities from 1lb/c.f. to 160/lb/c.f. and coatings with densities up to 250 lb/c.f.Based on the aforementioned typical preferred formulation for a rigidcoating with foam core, a 3/4 in. composite would have the followingspecifications as shown in Table III.

                  TABLE III                                                       ______________________________________                                        TYPICAL SPECIFICATIONS                                                                 Weight    Thick          Wgt  Vol                                    Layer    (lb/sf)   (in)    S.G.   (%)  (%)                                    ______________________________________                                        Top                                                                           Coating  .26       .04     1.2    11.8 5.3                                    Strands  .14       .01     2.5    6.4  1.3                                    Chopped  .05        .005   2.5    2.3   .07                                   Core     1.3       .64     0.4    59.0 86.66                                  Bottom                                                                        Chopped  .05        .005   2.5    2.3   .07                                   Strands  .14       .01     2.5    6.4  1.3                                    Coating  .26       .04     1.2    11.8 5.3                                    ______________________________________                                         Densities; Skin, 112 lb/c.f.                                                  Core, 25 lb/c.f.                                                         

With particular regard to flexure strength, it will be appreciated thatthe continuous strands 66, 68, being undirectional, contribute to theelastic modulus only in the longitudinal direction. The chopped strands70, 71 produce primarily strength in the transverse or cross webdirection as well as interlinking the coating 20 to the core 26. Thisresults in a composite of significantly increased flexure strength.

For example, without the chopped glass, the modulus of a 3/4 inch boardis equal to the core or about 70,000 psi for a typical 25 lb/c.f.material. However with the addition of chopped glass interface, theflexure modulus normally exceeds 1,500,000 psi for a deposit level of0.08 lb/s.f. A cross strand directional mat applied with thelongitudinal continuous glass strands provides elastic modulus in thetransverse board direction.

Depositing the chopped glass between and in both the skin 20 and thecore 26 substantially strengthens the chemical and mechanical bondbetween the skin 20 and the core 26. The strands which are embedded atone end in the core 26 and at the other end in the coating 20 areeffective in maintaining integrity during cyclical loading. This effectis illustrated in FIG. 5 more clearly. During deflection, there is ashear force at the interface of the skin and the core which acts toseparate the skin as demonstrated by the mode of failure in thecomposite. More particularly, the composite fails by shearing the corewith a resulting delamination of the skin from the core. Such failureoccurs when the strain due to deflection reaches some critical level inthe core. This demonstrates that the modulus of the coating and thenetwork is so high that the core will break in shear before the coatingwill fail.

During flexure, the top of the composite 10 is in compression while thebottom is in tension. During compression, the chopped glass functions asan array of high strength bridgings to restrain the separation of thehigh strength coating from the lower strength, low density core. This isshown in the comparative cases in Table IV, below:

                  TABLE IV                                                        ______________________________________                                        FLEXURAL STRENGTH OF COMPOSITES                                                         Flexure                                                                       Modulus  Thick     Density                                                                              Strain                                    Case No.  (psi)    (in)      (lb/cf)                                                                              (in)                                      ______________________________________                                        1. Core only                                                                            110,000  1.0       30     0.0054                                    2. Mat and                                                                              150,000  1.0       30     0.0074                                    chopped                                                                       core                                                                          3. Composite                                                                            1,700,000                                                                              1.0       30     0.0104                                    ______________________________________                                    

Case 1 is a 65% filled urethane core blown 4.2 times to form ahomogeneous part.

Case 2 is the same as Case 1 with the addition of a fiberglass matt with3/16 in. openings pressed into the surface of the core by the blowingaction in the mold.

Case 3 is the same as Case 1 with the chopped glass core and a highdensity skin with a three dimensional interface formed by continuousglass and chopped glass.

All tests were run on 9 inch centers using a molded part 4 inch by 12inch by 1 inch.

With reference to the glass mat of Case 2, it will be noted that themodulus is increased over the plain core of Case 1. In this instance thepart failed when the strain at the interface between the skin and thecore reached the critical value of the compression strength for thetested density. The strain at failure for a 65% calcium carbonate filledurethane ranges from 0.006 for a density of 83 lb/c.f. to 0.004 for adensity of 25 lb/c.f., with a 30 lb/c.f. having a strain of 0.005 in.

It will be noted that the mat improves the property of the foam core andcontributes to an increase in the strain at failure. At a strain of0.0074 at the outer surface of the coating, the part failed with a crackin the core resulting in a delamination. In this test the coating wasvisually ascertained to be approximately 0.125 inch. This correlatesquite closely with a theoretical calculation, determined as set forthbelow, of 0.102 inch. It also demonstrates that the chopped glass on theoutside of the core forms a composite network of skin on a core, in viewof the predicted core failure at 0.0059 inch.

In Case 3, the coating was a urethane coating applied in theaforementioned manner to the outside of the continuous and chopped glassstrands. The coating penetrated the strand and chopped glass. However,the coating remained substantially separated from the core by the glassinterface. This produced a hard, rigid skin bonded to the core by thebridging of the chopped glass strands.

Case 3 failed in the same mode as Case 2, i.e. shear failure of the corewith a resultant delamination of the coating. Visual inspectionindicated that the outer layer of the composite comprised the coating,strand glass embedded in the coating with chopped glass embedded in theinner surface thereof. However the delamination was not as clearlydefined as in Case 2 demonstrating that the chopped glass reinforced theinterface. In case 3 the core failure resulted toward the outer surfaceof the core in the vicinity of an area where the chopped glass hadlesser bridging networking with the skin, the location whereat thecritical value appears to have occurred.

Placing all of the chopped glass in the core instead of bridging thecore and the skin increases the flexure properties somewhat as indicatedby the results of Case 1 versus Case 2. In both cases, however, crackswere easily formed in the skin. This results because the skin is weak inthe cross strand direction, in the case of strand glass, and was brokenby the core in the case where the mat was used. Accordingly, if all thechopped glass remains in the skin, the strength of the skinperpendicular to the strand glass is enhanced but the interface betweenthe skin and the core is weaker. Therefore, a part under flexure failsat a lower loading because the skin is only held on by the adhesion ofthe foam to the skin. This is particularly important with respect to thetop surface of the composite which is in compression during flexure.

The above results lend themselves to equations which can be used todesign and predict flexure performance of products made in accordancewith the invention, particularly with respect to longer spans. Forshorter spans, an additional equation may be required to account fordeflection due to shear. To demonstrate the applicability of theequations set forth below, two samples were prepared for flexuretesting. In each the density of the core material was 24 lb/s.f.,equivalent to a core blow of 4.2 times. A urethane coating was appliedto the outside of the core at a rate of 0.26 lb/s.f. on top of 64strands of glass, 10×10⁶ psi modulus, at a coating thickness of 0.05inches. The integral bridge bond between the chopped glass and the skinsevered at an applied rate of 0.04 lb/s.f.

The first part was 3/4×12 inch in configuration. The second part was1×12 inch. The parts were flexure tested by loading at mid-span andsupported on 48 inch centers. This support length was selected to insurethat only flexure, and not shear, was the mode of failure. The graphicresults of the test are shown in FIG. 6.

On the basis of these results, the flexure strength can be predictedfrom two equations: ##EQU1##

wherein d is the critical deflection of the core, in inches; e is thecritical strain in the core where failure begins on the outermostsurface of the core; t is the core thickness, in inches; and L is thedistance of the spans, in inches. (This equation is applicable forsingle point loading and span as indicated by a comparison of the testand calculated values.) ##EQU2##

wherein d is the critical deflection of the composite, in inches; P isthe load at midspan, in pounds; h is the thickness of the composite, ininches; b is the width of the composite, in inches; E is the modulus ofelasticity of the skin, in psi; and t is the thickness of the skin, ininches.

These results show that the load and deflection are linerally relatedfrom zero to the critical deflection whereat the core cracks. Because ofthe chopped glass interlocking between the core and the skin, thedeflection continues until the load is sufficient to cause delamination.The foregoing results and the sensitivity of parameters indicate thatreproducibility of the products can be predicated on process control of:thickness of part, skin, core; part width, core and skin density; andcomposition.

The bidirectional strength of the composite may also be increased asdescribed above by incorporating transverse or cross continuous strandsin the composite. The cross continuous strands abut the longitudinalstrands and are located at the interface and interlocked with thebridging of the chopped glass. Preferably the cross strands aremanufactured from parallel strands of glass roving which are heldtogether by a fine woven cross thread thereby providing unidirectionalfibrous glass reinforcement in the warp direction. A suitable suchroving is available from Fiber Glass Industries, Inc. under the Foresilbrand. The cross strands are applied at rates comparable to thelongitudinal strands.

The contributions of such cross strands to birectional flexure strengthwas demonstrated in the following tests. Seven sample composites wereprepared with different combinations of structural components. Samplesizes were 4 inch by 4 inch by 3/4 inch. The samples were placed underthe three point loading and the weight for 1/4 inch deflection noted.The results are detailed in Table V.

                  TABLE 3                                                         ______________________________________                                        Component              Load                                                   No.    A       B     C     D   E     Y     X                                  ______________________________________                                        1.     x       --    --    --  --    240   240                                2.     x       x     --    --  --    480   480                                3.     x       x     x     --  --    590   590                                4.     x       x     x     x   --    760   1200                               5.     x       x     --    --  x     1080  480                                6.     x       x     x     --  x     1200  760                                7.     x       x     x     x   x     1370  1370                               ______________________________________                                         A. Core                                                                       B. Coating                                                                    C. Chopped glass                                                              D. Continuous glass in X direction                                            E. Continuous glass in Y direction                                       

From the foregoing it will be apparent that glass in the Y or transversedirection provides a substantial increase in the transverse flexuralstrength and and in combination with the core, coating, chopped glassand longitudinal glass provides uniform strength characteristics in bothdirections.

Operation of the Process

For the typical formulations described above as practiced in theillustrated apparatus and with reference thereto, initially the driveunits are energized to drive the belts 40, 42 through the enclosure 130.Sufficient hydraulic pressure is applied to the molds to maintainclosure under the foaming pressures. The speed of the molds iscontrolled to keep the mold fill rate constant as the drive power pullsthe molded composite continuously down the line toward the exit end 48.

The element 132 is energized to supply heat sufficient to preheat themolds to around 150-160 degrees F. The mold temperatures are tightlycontrolled to provide the optimum temperature for developing the desiredskin surface without melting the plastic film. As the coating 74 entersat 120 degrees F. or below, a temperature in the above range causes theskin to form immediately at the film-coating interface. As the composite10 proceeds downstream, the molds transfer heat to the coating 64,causing the reaction to proceed to completion. If the core 74 blowsbefore the coating forms a skin, it will force the glass, continuous andchopped, outwardly into the coating causing a breakup of the skin. Thisresults in a part with surface defects and lowered physical properties.

In this connection, it is important that the coating wet the glass as itmoves into the enclosure 130. The bottom strand glass is wetted beforeit enters the machine. The top glass is wetted when the weight of thecore material forces the strand glass into the coating.

Once the coating has set a skin, the core may commence rising. Asmentioned above, too much blow or too little blow is critical fordimensional stability. This exothermic reaction is effective to raisethe mold cavity temperatures to cause skinning of the coating withinZone A as shown in FIG. 3. Throughout the process, heating and coolingis supplied to maintain these conditions. Inasmuch as the reactions areexothermic, cooling is required under certain operating conditions.Under steady state operating conditions, a temperature range of 155-160degrees F is preferred with an exiting core temperature of about 170-180degrees F. Through suitable instrumentation, mold temperature monitoringand exit temperature monitoring provide substantial indication that thereactions are proceeding on schedule. Unless temperatures are maintainedin this range, product integrity suffers as reflected in poor qualitycomposite evidenced by holes in the coating, blow holes in the core, andlack of full core filling, particularly in the lower temperatures. Dropsin the temperatures beyond those briefly experienced at process start-upare indications of variations in chemistry and mechanical operation. Asmentioned above, the upper range represents the melting point of thefilm and if exceeded may cause adhesion to the product or the mold.

Further, unless the mold temperature is maintained, the criticalreactions of the core and coating will not balance. For instance, if thecoating sets prematurely before the core completes its blow, theexterior coating will not conform to the mold configuration. Conversely,if the coating is allowed to go uncured until the core completes itsblow, the coating will separate permitting intrusion of the core. Thislowers the strength and impairs the cosmetic appearance of the coatingexterior surface.

As shown in FIG. 3, at the entrance end of the apparatus, the coatings64,65 are applied directly to the polyethylene mold liner films 60, 62.The thickness of the coating is determined by the speed of the belts 40,42 and the delivery rate of the coating material. At this point thecoating has a viscosity in the range of 2,000 to 10,000 centipores,which may be controlled at the supply tank or at the supply lines byindirect heating methods.

The mold release film is at room temperature, such that the combinationof the film and the coating enters the machine at a preferredtemperature of around 100 degrees F. Once the film and the coatingcontact the heated molds, the temperature thereof rapidly increases andself skinning commences with a consequent rapid rise in the coatingviscosity. After application of both coatings, the continuous strandsand/or mats of fiberglass are applied to the coatings and the choppedglass is deposited on the lower coating and the upper surface of thefoam. As discussed above, the glass is not allowed to penetrate thecoating layer until the skinning has begun.

The core 74 is applied onto the glass after the coating. This preformenters the molds 40,42 at a line speed of around 20 ft/min. and the corebegins to blow at 12-15 seconds in Zone A. The blow is completed at40-50 seconds in Zone B. The blowing causes the wetting of thefiberglass by both reactant compositions and an incorporation of thereinforcement at the interface therebetween.

It will be appreciated that the concentration and type of catalyst willcontrol the reaction speed and accommodate differing formulations withinthe process. For instance, a 10% decrease in the coating formula willextend the reaction time by 20 seconds. A similar increase will causethe reaction time to decrease by 10-15 seconds. Nonetheless the criticalevents to control in Zone A, for the coating, are to achieve proper flowof the coating onto the film, a surface wetting of the glass andinitiation of the skinning reaction against the mold. At the core, theevents to control in Zone A are to ensure an even flow of corereactants, a wetting of the lower glass mat and a conforming of thecoating against the mold are required. More particularly, the lowviscosity coating wets at least the continuous glass strands and topenetrate the toward the chopped glass.

In Zone B, the foam reacts fully to fill the mold. If the foam does notrise sufficiently within this time, holes, soft spots, and voids areexperienced. There is also a consequent loss of dimensional control. Ifthe foam rises too much, the foam may roll back upon itself andseparating the molds to produce excess flashing. This increases thepower required to pull the composite through the machine. Under excessconditions, excessive foaming may result in stalling of the molds 40,42.

The desired density, the cream time, the gel time, and the rate of riseare controlled in Zone B through conventional urethane chemistry. Basicto this control is the metering of the blowing agent, catalysts andisocyanates. Too much core blow or not enough core blow in Zone B canchange the product dimensions. The proper blowing is achieved bycontrolling (1) the water to blowing catalyst ratio to the excessisocyanate and (2) the relationship of the flow of core onto the belt,and (3) belt speed. The ratio of water and catalyst is also controlledto achieve the desired small uniform cells. If the water to catalystratio is unbalanced, the part will fill the mold, but the cells will betoo large, resulting in decreased compressive and flexure strength.

Inasmuch as the blowing agent comprises water, the variation in thewater absorbed on the raw materials is a critical variable. As water isabout 5,000 times more reactive than the polyurethane such that smallchanges in absorbed moisture will significantly change the blowingconditions. The absorbed water is primarily dependent on environmentalconditions and accordingly constantly changing in response thereto.While calcium carbonate is a desirable filler for economic reasons, itsmoisture content is widely variable, ranging from about 0.1%. to 0.5% atambient conditions. This requires formulation adjustment to compensatefor these changes. The requisite adjustments may be accomplished byadjusting the overall formulation such that the absorbed moisture isused as the blowing agent with the balance of the required water beingsupplementally supplied through the meters.

Control as to the water content of the formulation is achieved bymonitoring the hardness of the parts exiting the machine as well as thedimensions thereof. If the overall absorbed moisture decreases forconstant supplemental water, the blow decrease and the effect is notedby dimensional change. In this event, additional water and catalyst mustbe added to return the product to specification. This is accomplished byadjusting the meters to bleed additional water and catalyst therebyestablishing the correct ratio. While the overall componentspecifications are established during product development to provide aset of desirable properties in the end product, the catalyst nonethelessmust be adjusted so that the molded product will skin immediately andbecome hardened before exiting the machine such that the finaldimensions are thereby constrained at the exit end. In Zone C, thereactants are partially cured resulting in a rigid coating, and ahardened foam Which is tack free and rigid, such that the composite 10is complete and ready for for the severing operation, with dimensionalstability. Final curing is effected in storage.

It is extremely important to ensure that a chemical bond and not merelyan adhesive bond is formed at the glass interface. This requires thatthe coating be in the reaction or tacky phase during the foaming suchthat the core will react with it. Thus the core should foam just priorto skin setting and not significantly before or after.

With further regard to the interface, the amount of chopped glass isimportant inasmuch as it defines a structural boundary and the modulusof the product. Too much chopped glass will permit the core to foam toone side and the skin to set at the other side, with little or nochemical bonding therebetween. The failure mode reveals unwetted choppedglass. Too little glass, on the other hand, will allow the chopped glassto contact the strand glass making it the interface. In accordance withthe present invention, the strongest products are made when the coatinghas time to wet the strand glass and lock some of the chopped glass intothe skin showing that the skin has been partially formed before the coreand that as the core rises to meet the skin it has incorporated aportion therewithin.

In order to keep the weight per foot constant, fill the molds andperform as aforementioned in each zone, the formulations are dynamicallychanged to compensate for the variations in materials. This is wellknown based on the various materials in contact with the isocyanate andthe hydroxal numbers associated therewith.

As previously discussed, fillers such as calcium carbonate may containabsorbed moisture which functions as a blowing agent in addition to theinjected water. Unless the material is dried beforehand, compensationmust be made by dynamically changing the water, the isocyanate level andthe catalyst level.

Such dynamic control is critical to the proper operation of the process.In other words, batch mixing of all the components may in certaininstances yield acceptable product, but steady state product quality isdifficult if not impossible to achieve. Batching in reality allowsprocess control only through belt speed, mold temperature, and theisocynate/polyol ratio.

Various modifications of the above-described embodiment will be apparentto those skilled in the art. Accordingly, the scope of the invention isdefined only by the accompanying claims.

What is claimed:
 1. A reinforced polymeric composite, comprising: a foamcore of a first polymeric composition; a skin surrounding said core of asecond polymeric composition; a three dimensional interface chemicallyand mechanically bonding said core to said skin comprising strands of ahigh modulus material including continuous longitudinal strandssubstantially uniformly peripherally spaced about the outer surface ofsaid core and the inner surface of said skin, continuous transversestrands substantially uniformly spaced along the length of said coreadjacent to said longitudinal strands, a transverse layer of firstchopped strands randomly contacting said longitudinal strands and saidtransverse strands, and second chopped strands inclined with respect tosaid core.
 2. The composite recited in claim 1 wherein third choppedstrands are randomly dispersed within said core.
 3. The compositerecited in claim 2 wherein said third chopped strands have a length ofaround one inch to two and one half inch.
 4. The composite recited inclaim 1 wherein said first polymeric composition is formed by a reactantmixture of a non-volatile liquid monomer, a surfactant and a catalyticsystem.
 5. The composite recited in claim 4 wherein said non-volatileliquid monomer is selected from the group consisting of polyurethanes,polyesters, polyamide, epoxies and acrylics.
 6. The composite recited inclaim 1 wherein said first and second chopped strands are depositedbetween about 0.02 pounds per square foot and 0.88 pounds per squarefoot.
 7. The composite recited in claim 1 wherein said first polymericcomposition comprises a rigid polyol composition including a reactantmixture of a polyol and isocyanate together with sufficient catalyst toeffect a rigid skin upon curing.
 8. The composite recited in claim 1wherein said second polymeric composition comprises a polyol, a filler,a blowing agent and catalyst in sufficient proportions to effect a rigidfoam composition upon curing.